<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
    <style type="text/css">
        canvas{
            border: 1px solid red;
        }
    </style>
</head>
<body>
<canvas id="box" width="800" height="800"></canvas>
<script type="text/javascript">
    var box=document.getElementById("box");
    var pen=box.getContext("2d");

     pen.translate(400,400);
//     for(var i=100;i>=20;i-=20){
//         pen.beginPath();
//         var a=Math.floor(Math.random()*255);
//         var b=Math.floor(Math.random()*255);
//         var c=Math.floor(Math.random()*255);
//         pen.arc(0,0,i,0,Math.PI*2);
//         pen.fillStyle="rgb("+a+","+b+","+c+")";
//         pen.fill();
//         pen.closePath();
//         pen.stroke();
//     }


     for(var i=1;i<=6;i++){
         pen.save();
         pen.scale(i,i);
         pen.beginPath();
         pen.arc(0,0,10,0,Math.PI*2);
         pen.restore();
         pen.closePath();
         pen.stroke();

     }





</script>
</body>
</html>